Diel fluctuations in Comanche Springs Pupfish Abundances in San Solomon Springs, Balmorhea State Park

Authors: Lauren Yancy, Joshuah Perkin, Matt Acre

Year: 2021

Abstract

The Comanche Springs Pupfish (Cyprinodon elegans) is a freshwater species only found in spring systems in the vicinity of Balmorhea, Texas in the Trans-Pecos region. The species was previously found in Comanche Springs in Fort Stockton, Texas until the springs ran dry because of groundwater depletion. The largest remaining population of Comanche Springs Pupfish occurs at Balmorhea State Park and is closely monitored and surveyed by the Texas Parks and Wildlife Department. The goal of this study was to assess diel behavior of the Comanche Springs Pupfish to test for diel variation consistent with the more widely studied Devils Hole Pupfish (Cyprinodon diabolis) that shows strong depth associations across gradients of light intensity. We hypothesized that Comanche Springs Pupfish abundance would be greater in shallow, concrete-bottom pool habitats during the day (when other fishes are absent) compared with night. To test this hypothesis, we conducted 9 repeated surveys (4 during the day; 5 at night) of pupfish abundance using a 1-m by 1-m quadrat to conduct visual counts along the shallow edge of San Solomon Pool. We then fit a generalized linear mixed model to predict pupfish abundance using space (distance from deep water) and time (day or night). We found significantly higher abundances of pupfish in the shallow water during the day compared with the night, supporting our initial hypothesis. Distance from deep water was not a statistically significant predictor of pupfish abundance. Our findings for Comanche Springs Pupfish show a reversed pattern of shallow water habitat use across the diel cycle compared with Devils Hole Pupfish, and therefore highlight variation in behaviors among pupfish species. The results of this study can be used by managers to identify ideal times to conduct visual-based population abundance counts that yield the most accurate results.